Modern gasoline and diesel engines develop damaging sludge and varnish deposits. These deposits are derived from fuel, oil, combustion by-products and entrapped water. The deposition problem is aggravated by high engine operating temperatures. Operating difficulties result when filters plug, valves stick, or when turbines become oil-starved. Ashless dispersants are commonly used to prevent sludge and varnish accumulations.
Ashless dispersants are, most commonly, reaction products of polyamines with either: (1) polybutylsuccinic anhydrides (to produce succinimides); or (2) polybutylphenol and formaldehyde (to produce Mannich bases, also termed Mannichs). These reactants or their reaction products are then reacted further with one or more acid, such as boric acid, or a fatty acid having 8-22 carbon atoms, such as oleic acid.
However, the polyamine reactants are costly and somewhat ineffective because low molecular weight polyamines, such as ethylene diamine, are disadvantageous, whereas higher molecular weight aliphatic polyamines frequently contain secondary nitrogen atoms which add to the nitrogen content while usually contributing relatively little to dispersancy.
Also, the secondary nitrogen atoms can remain unreacted and as such can contribute undesired basicity to the ashless dispersant. Excessive basicity tends to cause undesirable interactions with sulfonates and wear inhibitors. Fluoropolymer seals are degraded as well. By eliminating these secondary nitrogen atoms, this undesired basicity is reduced.